1. Field of the Invention
The present invention is directed to a circuit arrangement for measuring the current flowing between the anode and the filament in an x-ray tube.
2. Description of the Prior Art
In x-ray technology, the actual value of the x-ray tube current during the transillumination or exposure mode must be acquired for control purposes and must be converted into a corresponding voltage. For this purpose, it is known to connect a precision resistor in series with the high-voltage generator, at which the current signal is tapped. Due to the propagation constants per unit length of the high-voltage cable, signal parts that represent a dynamic (changing) falsification of the current signal are superimposed on this current signal given a change of the x-ray tube voltage. This effect occurs particularly when switching the x-ray tube on, since the x-ray tube voltage at that time is adjusted with its greatest rate of change, from zero to a prescribed nominal value. During the adjustment event of the x-ray tube voltage, a value of current is measured that lies clearly above the actual value. The reason for this dynamic superelevation of the value of the current is essentially the capacitance of the coaxial high-voltage cable, since a displacement current that cannot be left out of consideration flows into the cable capacitance given a high rate of change of the x-ray tube voltage.
German OS 34 47 490, corresponding to U.S. Pat. No. 4,670,893, discloses an arrangement wherein both the current acquired by a current detector and the voltage acquired by a voltage detector are processed in common in an x-ray tube. The problem of signal falsifications given changes of the x-ray tube voltage, however, still occurs.